Automatic rangefinder

ABSTRACT

Apparatus is disclosed for positioning an objective lens to focus an image of an object in a film plane which includes means for projecting a contrast pattern on the object, and a second lens for receiving and transmitting light reflected from the object to form an image of the contrast pattern upon a photocell. The photocell has a particular discernable output when the image is focused on the photocell. The apparatus also includes a mechanism for varying the distance between the second lens and the photocell to focus the image formed by the second lens upon the photocell and means responsive to the particular discernable output to position the objective lens so that the image of the object formed by the objective lens is focused in the film plane.

[ 51 Apr. 4, 11972 [54] AUTOMATIC RANGEFINDIER Donald M. ll-larvey,Webster, NY.

Eastman Kodak Company, Rochester, NY.

[22] Filed: Sept. 28, 1970 [21] Appl.No.: 76,081

[72] Inventor:

[73] Assignee:

Primary Examiner-Samuel ,Feinberg Assistant ExaminerS. C. BuczinskiAttorney-Robert W. Hampton and Raymond L. Owens [57] ABSTRACT Apparatusis disclosed for positioning an objective lens to focus an image of anobject in a film plane which includes means for projecting a contrastpattern on the object, and a second lens for receiving and transmittinglight reflected from the object to form an image of the contrast patternupon a photocell. The photocell has a particular discernable output whenthe image is focused on the photocell. The apparatus also includes amechanism for varying the distance between the second lens and thephotocell to focus the image formed by the second lens upon thephotocell and means responsive to the particular discemable output toposition the objective lens so that the image of the object formed bythe objective lens is focused in the film plane.

12 Claims, 6 Drawing Figures PATENTEDAPR 4 m2 3,653,762

sum 1 OF 2 (I) -l o r D. F D O V V I j LENS 22 DISPLACEMENT 3 FROM CELL44 6 I 1 f I (n I a P I '7! 6 1 I FIG. 4 1' u' IIA'Y l l I 44 is /T H--77 9 l 22 o r I l V I v I V 4 72 i d LENS 22 DISPLACEMENT 73 FROM CELL44 9O DONALD M. HARVEY INVENTOR.

BY @M QQM AT TORNE YS PATENTED APR 4 I972 SHEET 2 [IF 2 N SE DONALD M.HARVEY WWW ATTORNE Y5 AUTOMATIC RANGIEFINDER BACKGROUND OF THE INVENTIONThis invention relates to an automatic rangefinder and especially torangefinders suitable for use with cameras.

It has previously been recognized that when the relative distancebetween a photocell such as a sulfide or cadmium cell and a lens isvaried by moving the lens in an effort to focus an image of an objectonto the photocell, a perturbation occurs in the photocell electricaloutput as the lens passes through the position wherein the image isfocused on the photocell which is due to the property of such cells thatthey will exhibit different outputs for uniform and nonuniformdistributions of light over their surface, despite the fact that thetotal amount oflight remains a constant. This effect has been difficultto use inasmuch as in the instance of low contrast objects such as blankwalls, the effect is minimal'and extremely difficult to detect.

SUMMARY OF THE INVENTION In accordance with a disclosed embodiment ofthe invention, there is provided an objective lens which is adapted tofocus an image of an object in a film plane, and second and third lensesmounted so as to be movable in synchronism. An image having a contrastpattern is formed by the second lens on the object. Reflected lightwhich includes the contrast pattern is directed to a photocell by meansof the third lens. The second and third lenses are moved in synchronismuntil a perturbation is detected in the output of the photocell,indicating that the contrast of the reflected image is maximum and thatthe second lens is sharply focusing the image of the object on thephotocell. Means responsive to such perturbation are effective to focusthe objective lens. The invention, and its objects and advantages, willbecome more apparent in the detailed description of the preferredembodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS In the detailed description of thepreferred embodiment of the invention presented below, reference is madeto the accompanying drawings, in which:

FIG. 1 is a perspective view of a photographic camera including anexemplary automatic rangefinder of the type contemplated by theinvention;

FIG. 2 is a schematic showing of the overall automatic rangefinderapparatus which may be incorporated in the camera shown in FIG. 1;

FIG. 3 is a curve of the lens displacement vs. photocell outputrelationship for the apparatus of FIG. 2;

FIG. 4 is a schematic showing ofa lens assembly which may be used withthe FIG. 2 apparatus;

FIG. 5 is a schematic showing of another alternative lens assembly whichmay be used with the FIG. 2 apparatus; and

FIG. 6 is a curve showing the lens displacement vs. photocell outputrelationship prevailing for either lens assembly of FIGS. 4 or 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, anembodiment of the invention is disclosed in connection with a stillcamera 11 of general arrangement well known in the art and having theusual standard equipment including a viewfinder aperture 12, a filmwinding mechanism 13, an objective lens assembly 14, a shutter 42 (SeeFIG. 2), and a shutter release button 17. It will be understood that theinvention is equally applicable to movie cameras and other apparatus.

In accordance with the invention the camera 11 is provided withapertures 18 and 21 for a photocell lens 22 and a lens 23 (shown in FIG.2) respectively, and a motor start button 24, the functions of whichwill become apparent from the description which follows. Referring nowto FIG. 2, there is shown a rangefinder apparatus 25, including a lensassembly comprising the photocell lens 22 and the lens 23, mounted in asuitable carriage 27 which is movable forward and reverse (in thedirection of the arrows but within limits defined by stops 28a and 28bby an electric motor 28.

The lenses 22 and 23 are preferably identical and are supported by thecarriage 27 in duplex relationship so that during use of the camera,they are positioned substantially the same distance from the object 41,and they are movable in synchronism by the motor 28. The object 41 is ina line ofsight view of objective lens 14 of the camera 11. Reflectedlight from the object is projected by the lens 22 upon a photocell 44and the resulting output therefrom is provided as an input to suitablecircuitry described hereinafter, for controlling the motor 28 to focusthe image of the object 41 formed by the camera objective lens 14 in afilm plane F. For clarity of illustration some details of the camera 11have been omitted. For example, the lens 14 is, of course, disposedbetween the object 41 and the film plane F. The photocell 44 isadvantageously disposed along the lens axis of the lens 22 and is of ageneral class of devices wherein its electrical output is related to themagnitude and contrast of incident light such as the aforementionedsulfide or cadmium cells which have an electrical output which variesdirectly with the amount of light incident thereon, but also have thecharacteristic that their output changes when the distribution ofincident light varies even when the total incident light remains thesame. This phenomenon is characterized by the fact that the output willvary abruptly (viz. a perturbation) at the point where the cell is movedthrough a position when an image of an object is sharply focusedthereon.

In accordance with the invention, the perturbation effect is augmented.Towards this end, there is provided a suitable light source 47 withreflector 48 for projecting light rays through a plane-convex lens 51 tothe transmitting lens 23. In order to provide contrast to the object, atransparency 53 passes light which is directed to the object 41.Advantageously, the tra nsparency 53 is formed with a checkerboardpattern of light and dark areas. The projected light rays are pulsatedat a predetermined frequency either electrically or by suitablemechanical means such as the illustrated mechanical chopper 54 whichincreases the effectiveness of the apparatus 25, especially in theprocess of electrically detecting a perturbation in the output of thephotocell 44 as described later in this specification.

Advantageously, the transparency 53 and the photocell 44 are so disposedthat they occupy the same position relative to their respective lenses(viz. they are disposed at optical conjugate positions). Thus, when theprojected light which passes through the transparency forms a patternwhich is blurry when projected on the object 41, so too the reflectedimage is rendered even more blurry by the lens 22 when transmitted toform an image on the photocell 44. However, when both lenses are focusedat the same time and the contrast of the reflected image is a maximum,the perturbation effect is more pronounced at the output from thephotocell 44 inasmuch as the contrast of the image formed on the objectis a maximum. The photocell lens 22 may advantageously be provided witha centrally positioned stop means 57 to prevent the passage of allexcept the rim rays, which further enhances the perturbation effect.

The perturbation effect can be still further enhanced by improving thecontrast of the reflected image formed on the photocell 44. Towards thisend, there is provided a band pass optical filter represented by dottedline 58 which is designed to limit the emission spectrum of the light 47and the receiving spectrum of the photocell 44 to that portion of thelight spectrum to which the photocell 44 is most responsive. Thus, byreducing the general ambient light seen by the photocell, the signal tonoise output of the photocell 44 can be enhanced. This effect could alsobe achieved by placing the filter 58 only in front of the receiving lens22 although the illustrated arrangement is preferred.

To commence operation, the button 24 is depressed which may be arrangedto close contacts and apply a source of potential to the motor 28, lightsource 47, and a circuit 60 hereinafter described. The reflected imageof the object having the contrast pattern is formed by the lens 22 onthe photocell 44. The resulting electrical output of the photocell 44 involts, is discounting noise relatively smooth line curve (except at thebest focus position, see FIG. 3) and is applied to the circuit 60 whichincludes a band-pass filter 77, adapted to pass frequency componentscentered on the frequency of the chopper 54. The fileterd output is thenapplied to a current detector 78. The detector output is applied to aswitch network 81 which is designed to maintain a constant signal to anamplifier 82 so long as the photocell output remains on the smoothportion of the curve of FIG. 3, but functions to switch the amplifierOFF when perturbation in the photocell output occurs. The output fromamplifier 82 is applied as a driving voltage to the servo motor 28, andthus when it is cut off, it causes the motor 28 to stop.

The servo motor 28 may take various forms known in the art such as atraversing lead screw arrangement used for imparting transverse motionto such items as coil winders, line guides, or the like. Whateverarrangement is used, as the motor 28 is operated, lens carriage 27 ismoved back within the limits defined by stops 28a and 28b (shownschematically near the carriage 27) searching for the best focusposition and when it is found, the search is ended by stopping the motor28. The carriage is initially moved from a position corresponding toinfinity focus for the lens 22 (see point A on the curve of FIG. 3) tothe position wherein the lens 22 sharply focuses the image of the object41 on the photocell 44 and a perturbation occurs. At this position thecarriage is stopped. If a perturbation is not detected, then theobjective lens 14 should be disposed at an infinity focus position.

In order to focus the objective lens 14, the motor 28 is adapted torotate a lens adjusting cam 83 such that all of the lenses 22, 23, and14 will simultaneously be in focus when the perturbation is detected andthe motor stopped. Other means which are effective to focus the lens 14in response to the perturbation will undoubtedly suggest themselves tothose skilled in the art.

Referring in detail to FIG. 3, the illustrated curve is a typical lensdisplacement vs. cell output curve resulting when the carriage 27 ismoved. For sake of illustration, the curve is shown smooth and depicts agradual decrease in the cell output with lens displacement from theinfinity position a on the curve. This is, of course, due to the factthat the amount of light directed to the photocell 44 decreases as thelens 22 moves away from the photocell. However, a marked discontinuityor perturbation occurs in the curve as the lens passed through the pointof best or optimum focus indicated by dotted line f wherein the imageformed by the lens 22 on the photocell 44 is focused and the contrastpattern is a maximum. The provision of contrast to the light reflectedfrom the object 41 results in a readily detectable rise in the curve.The curve may, of course, not be completely smooth due to noise in theoutput of the cell 44, but this small ripple should not be enough toactuate the switch 81. Thus, where the term smooth is used, it will beunderstood to be used in a relative sense.

Turning now to an alternate lens assembly 90 shown in FIG. 4, there isprovided an arrangement for maintaining the acceptance angle for thephotocell 44 at a constant and thus maintain the amount of lightreceived by the photocell at a relative constant level. Towards thisend, the carriage 27 is provided with a gate 71 which is adapted to openthe viewing aperture as the lens carriage 27 moves the lens 22 away fromthe photocell from position a to position b".

Alternatively, a similar effect (viz. maintaining a constant angle 6)may be attained by use of a fixed stop 74 (FIG. 5) positioned betweenthe lens 22 and the photocell 44. For both of the embodiments of FIGS. 4and 5, the output of the photocell 44 will be a smooth, straight lineoutput curve (except for the best focus perturbation) such as shown inFIG. 6 will be realized. This type of an output will facilitatedetection by the circuitry 60 wherein the switch 81 may be aconventional threshold detector.

The invention has been described in detail with particular reference tothe preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1 claim:

1. In rangefinder apparatus for positioning an objective lens withrespect to a film plane to focus an image of an object'in the filmplane, the combination comprising:

a. means including a source of radiation for projecting on the object acontrast pattern;

b. photosensitive means adapted to produce an electrical output having aparameter related in magnitude to radiation received by saidphotosensitive means;

c. a second lens disposed to receive light reflected from the object toform a reflected image of at least a portion of the object and at leasta portion of said contrast pattern on said photosensitive means;

d. first means for varying the distance between said second lens andsaid photosensitive means to focus the image formed by said second lenson said photosensitive means; the output parameter of saidphotosensitive means being related to the magnitude and contrast of thereflected light and having a particular discernable output when thecontrast pattern is focused by said second lens on said photosensitivemeans; and

. second means coupled to said photosensitive means and responsive tosaid particular output for focusing the objective lens.

2. In rangefinder apparatus for positioning an objective lens withrespect to a film plane to focus an image of an object in the filmplane, the combination comprising:

a. means including a source of radiation pulsated at a predeterminedfrequency for projecting on the object a contrast pattern;

b. photosensitive means adapted to produce an electrical output having aparameter related in magnitude to radiation received by saidphotosensitive means;

c. a second lens disposed to receive light reflected from the object toform a reflected image of at least a portion of the object and saidcontrast pattern on said photosensitive means;

d. first means for varying the distance between said second lens andsaid photosensitive means to focus the image formed by said second lenson said photosensitive means; the output parameter of saidphotosensitive means being related to the magnitude of the reflectedlight and contrast and having a particular discemable output when thecontrast pattern is focused by said second lens on said photosensitivemeans;

e. second means coupled to said photosensitive means and adapted todetect said particular output and produce a signal; and

f. third means responsive to said detected output signal for focusingthe objective lens.

3. The invention as set forth in claim 2 wherein said second meansincludes circuitry having a band-pass filter centered on saidpredetermined frequency.

4. The invention as set forth in claim 3 wherein said projecting meansincludes a transparency disposed between said source of radiation andthe object.

5. In rangefinder apparatus for positioning an objective lens withrespect to a film plane to focus an image of an object in the filmplane, the combination comprising:

a. a source of radiation;

b. means including a second lens disposed in a cooperative relation withsaid radiation source for projecting an image having a contrast patternon the object;

c. photosensitive means adapted to produce an electrical output having aparameter related in magnitude to radiation received by saidphotosensitive means;

d. a third lens disposed to receive light reflected from the object toform a reflected image of at least a portion of the object and saidcontrast pattern on said photosensitive means;

e. first means for varying the distance between said objective lens andthe object and said second lens and said photosensitive means tosimultaneously focus the image formed by said second lens on the objectand the image formed by said third lens on said photosensitive means;the output parameter of said parameter of said photosensitive meansbeing related to the magnitude of the reflected light and having aparticular discernable output when the contrast pattern is focused bysaid second lens on said photosensitive means; and

f. means coupled to said photosensitive means and responsive to saidparticular output for focusing the objective lens.

6. The invention as set forth in claim 5 wherein said projecting meansincludes a transparency disposed between said source of radiation andthe object.

7. The invention as set forth in claim 6 wherein both said 7 second andthird lenses are substantially identical and are disposed to besubstantially the same distance from the object. 8. The invention as setforth in claim 6 wherein said detecting means includes circuitry havinga band-pass filter centered on said selected frequency.

9. The invention as set forth in claim 6 wherein said projecting meansincludes a transparency disposed between said source of radiation andthe object.

10. The invention as set forth in claim 9 wherein said transparency hasa checkerboard pattern.

11. The invention as set forth in claim 10 including means formaintaining the acceptance angle of said photosensitive means at aconstant.

12. In a rangefinder apparatus for finding the distance of an object,the combination comprising: photosensitive means having an electricaloutput related to the magnitude of incident radiant energy, a source ofradiation, means cooperative with said radiation source for projectingan image having a contrast pattern upon the object, a lens disposed incooperative relation with said photosensitive means for receivingradiation reflected from the object, means coupled to said lens forvarying the distance between said lens and the object to move said lensin relation to said photosensitive means through a position wherein saidlens focuses radiation reflected from the object including the contrastpattern to said photosensitive means, said photosensitive means having aparticular output when said lens is moved through said focus position,and means coupled to said photosensitive means and responsive to saidelectrical output for detecting said particular output.

1. In rangefinder apparatus for positioning an objective lens withrespect to a film plane to focus an image of an object in the filmplane, the combination comprising: a. means including a source ofradiation for projecting on the object a contrast pattern; b.photosensitive means adapted to produce an electrical output having aparameter related in magnitude to radiation received by saidphotosensitive means; c. a second lens disposed to receive lightreflected from the object to form a reflected image of at least aportion of the object and at least a portion of said contrast pattern onsaid photosensitive means; d. first means for varying the distancebetween said second lens and said photosensitive means to focus theimage formed by said second lens on said photosensitive means; theoutput parameter of said photosensitive means being related to themagnitude and contrast of the reflected light and having a particulardiscernable output when the contrast pattern is focused by said secondlens on said photosensitive means; and e. second means coupled to saidphotosensitive means and responsive to said particular output forfocusing the objective lens.
 2. In rangefinder apparatus for positioningan objective lens with respect to a film plane to focus an image of anobject in the film plane, the combination comprising: a. means includinga source of radiation pulsated at a predetermined frequency forprojecting on the object a contrast pattern; b. photosensitive meansadapted to produce an electrical output having a parameter related inmagnitude to radiation received by said photosensitive means; c. asecond lens disposed to receive light reflected from the object to forma reflected image of at least a portion of the object and said contrastpattern on said photosensitive means; d. first means for varying thedistance between said second lens and said photosensitive means to focusthe image formed by said second lens on saiD photosensitive means; theoutput parameter of said photosensitive means being related to themagnitude of the reflected light and contrast and having a particulardiscernable output when the contrast pattern is focused by said secondlens on said photosensitive means; e. second means coupled to saidphotosensitive means and adapted to detect said particular output andproduce a signal; and f. third means responsive to said detected outputsignal for focusing the objective lens.
 3. The invention as set forth inclaim 2 wherein said second means includes circuitry having a band-passfilter centered on said predetermined frequency.
 4. The invention as setforth in claim 3 wherein said projecting means includes a transparencydisposed between said source of radiation and the object.
 5. Inrangefinder apparatus for positioning an objective lens with respect toa film plane to focus an image of an object in the film plane, thecombination comprising: a. a source of radiation; b. means including asecond lens disposed in a cooperative relation with said radiationsource for projecting an image having a contrast pattern on the object;c. photosensitive means adapted to produce an electrical output having aparameter related in magnitude to radiation received by saidphotosensitive means; d. a third lens disposed to receive lightreflected from the object to form a reflected image of at least aportion of the object and said contrast pattern on said photosensitivemeans; e. first means for varying the distance between said objectivelens and the object and said second lens and said photosensitive meansto simultaneously focus the image formed by said second lens on theobject and the image formed by said third lens on said photosensitivemeans; the output parameter of said parameter of said photosensitivemeans being related to the magnitude of the reflected light and having aparticular discernable output when the contrast pattern is focused bysaid second lens on said photosensitive means; and f. means coupled tosaid photosensitive means and responsive to said particular output forfocusing the objective lens.
 6. The invention as set forth in claim 5wherein said projecting means includes a transparency disposed betweensaid source of radiation and the object.
 7. The invention as set forthin claim 6 wherein both said second and third lenses are substantiallyidentical and are disposed to be substantially the same distance fromthe object.
 8. The invention as set forth in claim 6 wherein saiddetecting means includes circuitry having a band-pass filter centered onsaid selected frequency.
 9. The invention as set forth in claim 6wherein said projecting means includes a transparency disposed betweensaid source of radiation and the object.
 10. The invention as set forthin claim 9 wherein said transparency has a checkerboard pattern.
 11. Theinvention as set forth in claim 10 including means for maintaining theacceptance angle of said photosensitive means at a constant.
 12. In arangefinder apparatus for finding the distance of an object, thecombination comprising: photosensitive means having an electrical outputrelated to the magnitude of incident radiant energy, a source ofradiation, means cooperative with said radiation source for projectingan image having a contrast pattern upon the object, a lens disposed incooperative relation with said photosensitive means for receivingradiation reflected from the object, means coupled to said lens forvarying the distance between said lens and the object to move said lensin relation to said photosensitive means through a position wherein saidlens focuses radiation reflected from the object including the contrastpattern to said photosensitive means, said photosensitive means having aparticular output when said lens is moved through said focus position,and means coupled to said photosensitive means and responsive to saidelectrical output for detecting said paRticular output.